Special Issue "X-Ray Free-Electron Laser"

A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Optics and Lasers".

Deadline for manuscript submissions: closed (31 March 2017)

Special Issue Editor

Guest Editor
Prof. Dr. Kiyoshi Ueda

Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan
Website | E-Mail
Interests: electron dynamics; molecular dynamics; atoms, molecules and clusters; ultrafast phenomena; photoionization; molecular imaging; electron spectroscopy; many particle spectroscopy; coherent control; free electron lasers

Special Issue Information

Dear Colleagues,

During the last decade, the advent of the x-ray free electron lasers (XFELs) has opened a new research avenue for investigations of ultrafast electron and structure dynamics in any form of matter. XFELs deliver coherent x-ray pulses, combining unprecedented power densities up to 1020 W/cm2 and extremely short pulse durations down to a few femtoseconds, offering important advantages over conventional x-ray sources for many applications. Time-resolved spectroscopic and structure studies on the timescale of femtoseconds allow us to probe electrons and atoms in action. Indeed, XFELs have been applied to study ultrafast charge transfer in a molecule and a molecular complex, chemical bond breaking and formation, and phase transitions in solids. The intense coherent XFEL pulse focused down to 1 mm2 makes single-shot diffraction imaging of non-crystalized biomolecules and nano-size objects reality. On the other hand, since the XFEL pulses are entering a new regime of x-ray intensities, they are opening a new research field of studying interaction between intense x-ray pulses and various forms of matters. The extremely intense x-ray pulse strips off so many electrons from an isolated atom, leads to a violent Coulomb explosion of an isolated molecule, and transforms a solid target into extremely dense plasma. Furthermore, rapidly developing XFEL technologies make, not only fully coherent x-ray pulses available routinely, but also pulse shaping and phase-controlling of multicolor pulses reality, opening another novel research area of x-ray non-linear spectroscopy and attosecond coherent control.

The Special Issue of the journal Applied Sciences, “X-ray free electron lasers”, aims to cover recent advances in the development of XFELs and in the applications of XFELs in the field of physics, chemistry, and biology, as well as relevant theoretical studies in the fields.

Prof. Dr. Kiyoshi Ueda
Guest Editor

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Published Papers (25 papers)

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Open AccessFeature PaperArticle A Dispersive Inelastic X-ray Scattering Spectrometer for Use at X-ray Free Electron Lasers
Appl. Sci. 2017, 7(9), 899; doi:10.3390/app7090899
Received: 14 July 2017 / Revised: 25 August 2017 / Accepted: 26 August 2017 / Published: 1 September 2017
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Abstract
We report on the application of a short working distance von Hamos geometry spectrometer to measure the inelastic X-ray scattering (IXS) signals from solids and liquids. In contrast to typical IXS instruments where the spectrometer geometry is fixed and the incoming beam energy
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We report on the application of a short working distance von Hamos geometry spectrometer to measure the inelastic X-ray scattering (IXS) signals from solids and liquids. In contrast to typical IXS instruments where the spectrometer geometry is fixed and the incoming beam energy is scanned, the von Hamos geometry allows measurements to be made using a fixed optical arrangement with no moving parts. Thanks to the shot-to-shot capability of the spectrometer setup, we anticipate its application for the IXS technique at X-ray free electron lasers (XFELs). We discuss the capability of the spectrometer setup for IXS studies in terms of efficiency and required total incident photon flux for a given signal-to-noise ratio. The ultimate energy resolution of the spectrometer, which is a key parameter for IXS studies, was measured to the level of 150 meV at short crystal radius thanks to the application of segmented crystals for X-ray diffraction. The short working distance is a key parameter for spectrometer efficiency that is necessary to measure weak IXS signals. Full article
(This article belongs to the Special Issue X-Ray Free-Electron Laser)
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Open AccessArticle Modeling Non-Equilibrium Dynamics and Saturable Absorption Induced by Free Electron Laser Radiation
Appl. Sci. 2017, 7(8), 814; doi:10.3390/app7080814
Received: 31 May 2017 / Revised: 22 July 2017 / Accepted: 27 July 2017 / Published: 9 August 2017
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Abstract
Currently available X-ray and extreme ultraviolet free electron laser (FEL) sources provide intense ultrashort photon pulses. Those sources open new exciting perspectives for experimental studies of ultrafast non-equilibrium processes at the nanoscale in condensed matter. Theoretical approaches and computer simulations are being developed
[...] Read more.
Currently available X-ray and extreme ultraviolet free electron laser (FEL) sources provide intense ultrashort photon pulses. Those sources open new exciting perspectives for experimental studies of ultrafast non-equilibrium processes at the nanoscale in condensed matter. Theoretical approaches and computer simulations are being developed to understand the complicated dynamical processes associated with the interaction of FEL pulses with matter. In this work, we present the results of the application of a simplified three-channel model to the non-equilibrium dynamics of ultrathin aluminum films excited by FEL radiation at 33.3, 37 and 92 eV photon energy. The model includes semi-classical rate equations coupled with the equation of propagation of the photon wave packets. X-ray transmission measurements are found to be in agreement with present simulations, which are also able to shed light on temporal dynamics (in the fs range) in nano-sized Al films strongly interacting with the photon pulse. We also expanded our non-linear model, explicitly including the two-photon absorption cross-section and the effect of including electron heating for reproducing transmission measurements. Full article
(This article belongs to the Special Issue X-Ray Free-Electron Laser)
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Open AccessFeature PaperArticle SwissFEL: The Swiss X-ray Free Electron Laser
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Appl. Sci. 2017, 7(7), 720; doi:10.3390/app7070720
Received: 13 June 2017 / Revised: 29 June 2017 / Accepted: 30 June 2017 / Published: 14 July 2017
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Abstract
The SwissFEL X-ray Free Electron Laser (XFEL) facility started construction at the Paul Scherrer Institute (Villigen, Switzerland) in 2013 and will be ready to accept its first users in 2018 on the Aramis hard X-ray branch. In the following sections we will summarize
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The SwissFEL X-ray Free Electron Laser (XFEL) facility started construction at the Paul Scherrer Institute (Villigen, Switzerland) in 2013 and will be ready to accept its first users in 2018 on the Aramis hard X-ray branch. In the following sections we will summarize the various aspects of the project, including the design of the soft and hard X-ray branches of the accelerator, the results of SwissFEL performance simulations, details of the photon beamlines and experimental stations, and our first commissioning results. Full article
(This article belongs to the Special Issue X-Ray Free-Electron Laser)
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Open AccessArticle Observing Femtosecond Fragmentation Using Ultrafast X-ray-Induced Auger Spectra
Appl. Sci. 2017, 7(7), 681; doi:10.3390/app7070681
Received: 11 June 2017 / Revised: 26 June 2017 / Accepted: 28 June 2017 / Published: 1 July 2017
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Abstract
Molecules often fragment after photoionization in the gas phase. Usually, this process can only be investigated spectroscopically as long as there exists electron correlation between the photofragments. Important parameters, like their kinetic energy after separation, cannot be investigated. We are reporting on a
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Molecules often fragment after photoionization in the gas phase. Usually, this process can only be investigated spectroscopically as long as there exists electron correlation between the photofragments. Important parameters, like their kinetic energy after separation, cannot be investigated. We are reporting on a femtosecond time-resolved Auger electron spectroscopy study concerning the photofragmentation dynamics of thymine. We observe the appearance of clearly distinguishable signatures from thymine′s neutral photofragment isocyanic acid. Furthermore, we observe a time-dependent shift of its spectrum, which we can attribute to the influence of the charged fragment on the Auger electron. This allows us to map our time-dependent dataset onto the fragmentation coordinate. The time dependence of the shift supports efficient transformation of the excess energy gained from photoionization into kinetic energy of the fragments. Our method is broadly applicable to the investigation of photofragmentation processes. Full article
(This article belongs to the Special Issue X-Ray Free-Electron Laser)
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Open AccessArticle State-Population Narrowing Effect in Two-Photon Absorption for Intense Hard X-ray Pulses
Appl. Sci. 2017, 7(7), 653; doi:10.3390/app7070653
Received: 29 April 2017 / Revised: 16 June 2017 / Accepted: 21 June 2017 / Published: 24 June 2017
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Abstract
We report on studies of state-populations during the two-photon absorption process using intense X-ray pulses. The calculations were performed in a time-dependent manner using a simple three-level model expressed by coupled rate equations. We show that the proposed approach describes well the measured
[...] Read more.
We report on studies of state-populations during the two-photon absorption process using intense X-ray pulses. The calculations were performed in a time-dependent manner using a simple three-level model expressed by coupled rate equations. We show that the proposed approach describes well the measured rates of X-rays excited in the one-photon and two-photon absorption processes, and allows detailed investigation of the state population dynamics during the course of the incident X-ray pulse. Finally, we demonstrate that the nonlinear interaction of X-ray pulses with atoms leads to a time-narrowing of state populations. This narrowing-effect is attributed to a quadratic incidence X-ray intensity dependence characteristic for nonlinear interactions of photons with matter. Full article
(This article belongs to the Special Issue X-Ray Free-Electron Laser)
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Open AccessArticle Algorithm for Reconstruction of 3D Images of Nanorice Particles from Diffraction Patterns of Two Particles in Independent Random Orientations with an X-ray Laser
Appl. Sci. 2017, 7(7), 646; doi:10.3390/app7070646
Received: 31 March 2017 / Revised: 8 June 2017 / Accepted: 8 June 2017 / Published: 23 June 2017
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Abstract
The method of angular correlations recovers quantities from diffraction patterns of randomly oriented particles, as expected to be measured with an X-ray free electron laser (XFEL), proportional to quadratic functions of the spherical harmonic expansion coefficients of the diffraction volume of a single
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The method of angular correlations recovers quantities from diffraction patterns of randomly oriented particles, as expected to be measured with an X-ray free electron laser (XFEL), proportional to quadratic functions of the spherical harmonic expansion coefficients of the diffraction volume of a single particle. We have previously shown that it is possible to reconstruct a randomly oriented icosahedral or helical virus from the average over all measured diffraction patterns of such correlations. We point out in this paper that a structure of even simpler particles of 50 Å or so in diameter and consisting of heavier atomic elements (to enhance scattering) that has been used as a test case for reconstructions from XFEL diffraction patterns can also be solved by this technique. Even though there has been earlier work on similar objects (prolate spheroids), one advantage of the present technique is its potential to also work with diffraction patterns not only due to single particles as has been suggested on the basis on nonoverlapping delta functions of angular scattering. Accordingly, we calculated from the diffraction patterns the angular momentum expansions of the pair correlations and triple correlations for general particle images and reconstructed those images in the standard way. Although the images looked pretty much the same, it is not totally clear to us that the angular correlations are exactly the same as different numbers of particles due to the possibility of constructive or destructive interference between the scattered waves from different particles. It is of course known that, for a large number of particles contributing to a diffraction parttern, the correlations converge to that of a single particle. It could be that the lack of perfect agreement between the images reconstructed with one and two particles is due to uncancelling constructive and destructive conditions that are not found in the case of solution scattering. Full article
(This article belongs to the Special Issue X-Ray Free-Electron Laser)
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Open AccessArticle FERMI: Present and Future Challenges
Appl. Sci. 2017, 7(6), 640; doi:10.3390/app7060640
Received: 12 May 2017 / Revised: 12 June 2017 / Accepted: 12 June 2017 / Published: 21 June 2017
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Abstract
We present an overview of the FERMI (acronym of Free Electron laser Radiation for Multidisciplinary Investigations) seeded free electron laser (FEL) facility located at the Elettra laboratory in Trieste. FERMI is now in user operation with both the FEL lines FEL-1 and FEL-2,
[...] Read more.
We present an overview of the FERMI (acronym of Free Electron laser Radiation for Multidisciplinary Investigations) seeded free electron laser (FEL) facility located at the Elettra laboratory in Trieste. FERMI is now in user operation with both the FEL lines FEL-1 and FEL-2, covering the wavelength range between 100 nm and 4 nm. The seeding scheme adopted for photon pulse production makes FERMI unique worldwide and allows the extension of table top laser experiments in the extreme ultraviolet/soft X-ray region. In this paper, we discuss how advances in the performance of the FELs, with respect to coherent control and multi-colour pulse production, may push the development of original experimental strategies to study non-equilibrium behaviour of matter at the attosecond-nanometer time-length scales. This will have a tremendous impact as an experimental tool to investigate a large array of phenomena ranging from nano-dynamics in complex materials to phenomena that are at the heart of the conversion of light into other forms of energy. Full article
(This article belongs to the Special Issue X-Ray Free-Electron Laser)
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Open AccessArticle Application of Matched-Filter Concepts to Unbiased Selection of Data in Pump-Probe Experiments with Free Electron Lasers
Appl. Sci. 2017, 7(6), 621; doi:10.3390/app7060621
Received: 27 April 2017 / Revised: 6 June 2017 / Accepted: 9 June 2017 / Published: 16 June 2017
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Abstract
Pump-probe experiments are commonly used at Free Electron Lasers (FEL) to elucidate the femtosecond dynamics of atoms, molecules, clusters, liquids and solids. Maximizing the signal-to-noise ratio of the measurements is often a primary need of the experiment, and the aggregation of repeated, rapid,
[...] Read more.
Pump-probe experiments are commonly used at Free Electron Lasers (FEL) to elucidate the femtosecond dynamics of atoms, molecules, clusters, liquids and solids. Maximizing the signal-to-noise ratio of the measurements is often a primary need of the experiment, and the aggregation of repeated, rapid, scans of the pump-probe delay is preferable to a single long-lasting scan. The limited availability of beamtime makes it impractical to repeat measurements indiscriminately, and the large, rapid flow of single-shot data that need to be processed and aggregated into a dataset, makes it difficult to assess the quality of a measurement in real time. In post-analysis it is then necessary to devise unbiased criteria to select or reject datasets, and to assign the weight with which they enter the analysis. One such case was the measurement of the lifetime of Intermolecular Coulombic Decay in the weakly-bound neon dimer. We report on the method we used to accomplish this goal for the pump-probe delay scans that constitute the core of the measurement; namely we report on the use of simple auto- and cross-correlation techniques based on the general concept of “matched filter”. We are able to unambiguously assess the signal-to-noise ratio (SNR) of each scan, which then becomes the weight with which a scan enters the average of multiple scans. We also observe a clear gap in the values of SNR, and we discard all the scans below a SNR of 0.45. We are able to generate an average delay scan profile, suitable for further analysis: in our previous work we used it for comparison with theory. Here we argue that the method is sufficiently simple and devoid of human action to be applicable not only in post-analysis, but also for the real-time assessment of the quality of a dataset. Full article
(This article belongs to the Special Issue X-Ray Free-Electron Laser)
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Open AccessArticle Terawatt-Isolated Attosecond X-ray Pulse Using a Tapered X-ray Free Electron Laser
Appl. Sci. 2017, 7(6), 614; doi:10.3390/app7060614
Received: 30 March 2017 / Revised: 29 May 2017 / Accepted: 8 June 2017 / Published: 13 June 2017
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Abstract
High power attosecond (as) X-ray pulses are in great demand for ultrafast dynamics and high resolution microscopy. We numerically demonstrate the generation of a ~230 attosecond, 1.5 terawatt (TW) pulse at a photon energy of 1 keV, and a 115 attosecond, 1.2 TW
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High power attosecond (as) X-ray pulses are in great demand for ultrafast dynamics and high resolution microscopy. We numerically demonstrate the generation of a ~230 attosecond, 1.5 terawatt (TW) pulse at a photon energy of 1 keV, and a 115 attosecond, 1.2 TW pulse at a photon energy of 12.4 keV, using the realistic electron beam parameters such as those of Korean X-ray free electron laser (XFEL) in a tapered undulator configuration. To compensate the energy loss of the electron beam and maximize its radiation power, a tapering is introduced in the downstream section of the undulator. It is found that the tapering helps in not only amplifying a target radiation pulse but also suppressing the growth of satellite radiation pulses. Tapering allows one to achieve a terawatt-attosecond pulse only with a 60 m long undulator. Such an attosecond X-ray pulse is inherently synchronized to a driving optical laser pulse; hence, it is well suited for the pump-probe experiments for studying the electron dynamics in atoms, molecules, and solids on the attosecond time-scale. For the realization of these experiments, a high level of synchronization up to attosecond precision between optical laser and X-ray pulse is demanded, which can be possible by using an interferometric feedback loop. Full article
(This article belongs to the Special Issue X-Ray Free-Electron Laser)
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Open AccessFeature PaperArticle Photon Beam Transport and Scientific Instruments at the European XFEL
Appl. Sci. 2017, 7(6), 592; doi:10.3390/app7060592
Received: 1 May 2017 / Revised: 31 May 2017 / Accepted: 1 June 2017 / Published: 9 June 2017
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Abstract
European XFEL is a free-electron laser (FEL) user facility providing soft and hard X-ray FEL radiation to initially six scientific instruments. Starting user operation in fall 2017 European XFEL will provide new research opportunities to users from science domains as diverse as physics,
[...] Read more.
European XFEL is a free-electron laser (FEL) user facility providing soft and hard X-ray FEL radiation to initially six scientific instruments. Starting user operation in fall 2017 European XFEL will provide new research opportunities to users from science domains as diverse as physics, chemistry, geo- and planetary sciences, materials sciences or biology. The unique feature of European XFEL is the provision of high average brilliance in the soft and hard X-ray regime, combined with the pulse properties of FEL radiation of extreme peak intensities, femtosecond pulse duration and high degree of coherence. The high average brilliance is achieved through acceleration of up to 27,000 electron bunches per second by the super-conducting electron accelerator. Enabling the usage of this high average brilliance in user experiments is one of the major instrumentation drivers for European XFEL. The radiation generated by three FEL sources is distributed via long beam transport systems to the experiment hall where the scientific instruments are located side-by-side. The X-ray beam transport systems have been optimized to maintain the unique features of the FEL radiation which will be monitored using build-in photon diagnostics. The six scientific instruments are optimized for specific applications using soft or hard X-ray techniques and include integrated lasers, dedicated sample environment, large area high frame rate detector(s) and computing systems capable of processing large quantities of data. Full article
(This article belongs to the Special Issue X-Ray Free-Electron Laser)
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Open AccessCommunication Measurement of the X-ray Spectrum of a Free Electron Laser with a Wide-Range High-Resolution Single-Shot Spectrometer
Appl. Sci. 2017, 7(6), 584; doi:10.3390/app7060584
Received: 31 March 2017 / Revised: 24 May 2017 / Accepted: 30 May 2017 / Published: 6 June 2017
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Abstract
We developed a single-shot X-ray spectrometer for wide-range high-resolution measurements of Self-Amplified Spontaneous Emission (SASE) X-ray Free Electron Laser (XFEL) pulses. The spectrometer consists of a multi-layer elliptical mirror for producing a large divergence of 22 mrad around 9070 eV and a silicon
[...] Read more.
We developed a single-shot X-ray spectrometer for wide-range high-resolution measurements of Self-Amplified Spontaneous Emission (SASE) X-ray Free Electron Laser (XFEL) pulses. The spectrometer consists of a multi-layer elliptical mirror for producing a large divergence of 22 mrad around 9070 eV and a silicon (553) analyzer crystal. We achieved a wide energy range of 55 eV with a fine spectral resolution of 80 meV, which enabled the observation of a whole SASE-XFEL spectrum with fully-resolved spike structures. We found that a SASE-XFEL pulse has around 60 longitudinal modes with a pulse duration of 7.7 ± 1.1 fs. Full article
(This article belongs to the Special Issue X-Ray Free-Electron Laser)
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Open AccessArticle Split-And-Delay Unit for FEL Interferometry in the XUV Spectral Range
Appl. Sci. 2017, 7(6), 544; doi:10.3390/app7060544
Received: 29 March 2017 / Revised: 5 May 2017 / Accepted: 22 May 2017 / Published: 25 May 2017
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Abstract
In this work we present a reflective split-and-delay unit (SDU) developed for interferometric time-resolved experiments utilizing an (extreme ultraviolet) XUV pump–XUV probe scheme with focused free-electron laser beams. The developed SDU overcomes limitations for phase-resolved measurements inherent to conventional two-element split mirrors by
[...] Read more.
In this work we present a reflective split-and-delay unit (SDU) developed for interferometric time-resolved experiments utilizing an (extreme ultraviolet) XUV pump–XUV probe scheme with focused free-electron laser beams. The developed SDU overcomes limitations for phase-resolved measurements inherent to conventional two-element split mirrors by a special design using two reflective lamellar gratings. The gratings produce a high-contrast interference signal controlled by the grating displacement in every diffraction order. The orders are separated in the focal plane of the focusing optics, which enables one to avoid phase averaging by spatially selective detection of a single interference state of the two light fields. Interferometry requires a precise relative phase control of the light fields, which presents a challenge at short wavelengths. In our setup the phase delay is determined by an in-vacuum white light interferometer (WLI) that monitors the surface profile of the SDU in real time and thus measures the delay for each laser shot. The precision of the WLI is 1 nm as determined by optical laser interferometry. In the presented experimental geometry it corresponds to a time delay accuracy of 3 as, which enables phase-resolved XUV pump–XUV probe experiments at free-electron laser (FEL) repetition rates up to 60 Hz. Full article
(This article belongs to the Special Issue X-Ray Free-Electron Laser)
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Open AccessArticle Fundamental Limits on Spatial Resolution in Ultrafast X-ray Diffraction
Appl. Sci. 2017, 7(6), 534; doi:10.3390/app7060534
Received: 7 April 2017 / Revised: 16 May 2017 / Accepted: 17 May 2017 / Published: 23 May 2017
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Abstract
X-ray Free-Electron Lasers have made it possible to record time-sequences of diffraction images to determine changes in molecular geometry during ultrafast photochemical processes. Using state-of-the-art simulations in three molecules (deuterium, ethylene, and 1,3-cyclohexadiene), we demonstrate that the nature of the nuclear wavepacket initially
[...] Read more.
X-ray Free-Electron Lasers have made it possible to record time-sequences of diffraction images to determine changes in molecular geometry during ultrafast photochemical processes. Using state-of-the-art simulations in three molecules (deuterium, ethylene, and 1,3-cyclohexadiene), we demonstrate that the nature of the nuclear wavepacket initially prepared by the pump laser, and its subsequent dispersion as it propagates along the reaction path, limits the spatial resolution attainable in a structural dynamics experiment. The delocalization of the wavepacket leads to a pronounced damping of the diffraction signal at large values of the momentum transfer vector q, an observation supported by a simple analytical model. This suggests that high-q measurements, beyond 10–15 Å 1 , provide scant experimental payback, and that it may be advantageous to prioritize the signal-to-noise ratio and the time-resolution of the experiment as determined by parameters such as the repetition-rate, the photon flux, and the pulse durations. We expect these considerations to influence future experimental designs, including source development and detection schemes. Full article
(This article belongs to the Special Issue X-Ray Free-Electron Laser)
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Open AccessArticle X-ray Pump–Probe Investigation of Charge and Dissociation Dynamics in Methyl Iodine Molecule
Appl. Sci. 2017, 7(5), 529; doi:10.3390/app7050529
Received: 26 April 2017 / Revised: 15 May 2017 / Accepted: 15 May 2017 / Published: 19 May 2017
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Abstract
Molecular dynamics is of fundamental interest in natural science research. The capability of investigating molecular dynamics is one of the various motivations for ultrafast optics. We present our investigation of photoionization and nuclear dynamics in methyl iodine (CH3I) molecule with an
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Molecular dynamics is of fundamental interest in natural science research. The capability of investigating molecular dynamics is one of the various motivations for ultrafast optics. We present our investigation of photoionization and nuclear dynamics in methyl iodine (CH3I) molecule with an X-ray pump X-ray probe scheme. The pump–probe experiment was realized with a two-mirror X-ray split and delay apparatus. Time-of-flight mass spectra at various pump–probe delay times were recorded to obtain the time profile for the creation of high charge states via sequential ionization and for molecular dissociation. We observed high charge states of atomic iodine up to 29+, and visualized the evolution of creating these high atomic ion charge states, including their population suppression and enhancement as the arrival time of the second X-ray pulse was varied. We also show the evolution of the kinetics of the high charge states upon the timing of their creation during the ionization-dissociation coupled dynamics. We demonstrate the implementation of X-ray pump–probe methodology for investigating X-ray induced molecular dynamics with femtosecond temporal resolution. The results indicate the footprints of ionization that lead to high charge states, probing the long-range potential curves of the high charge states. Full article
(This article belongs to the Special Issue X-Ray Free-Electron Laser)
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Open AccessArticle Probing Dynamics in Colloidal Crystals with Pump-Probe Experiments at LCLS: Methodology and Analysis
Appl. Sci. 2017, 7(5), 519; doi:10.3390/app7050519
Received: 4 April 2017 / Revised: 4 May 2017 / Accepted: 8 May 2017 / Published: 19 May 2017
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Abstract
We present results of the studies of dynamics in colloidal crystals performed by pump-probe experiments using an X-ray free-electron laser (XFEL). Colloidal crystals were pumped with an infrared laser at a wavelength of 800 nm with varying power and probed by XFEL pulses
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We present results of the studies of dynamics in colloidal crystals performed by pump-probe experiments using an X-ray free-electron laser (XFEL). Colloidal crystals were pumped with an infrared laser at a wavelength of 800 nm with varying power and probed by XFEL pulses at an energy of 8 keV with a time delay up to 1000 ps. The positions of the Bragg peaks, and their radial and azimuthal widths were analyzed as a function of the time delay. The spectral analysis of the data did not reveal significant enhancement of frequencies expected in this experiment. This allowed us to conclude that the amplitude of vibrational modes excited in colloidal crystals was less than the systematic error caused by the noise level. Full article
(This article belongs to the Special Issue X-Ray Free-Electron Laser)
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Open AccessFeature PaperArticle Construction and Commissioning of PAL-XFEL Facility
Appl. Sci. 2017, 7(5), 479; doi:10.3390/app7050479
Received: 23 March 2017 / Revised: 20 April 2017 / Accepted: 26 April 2017 / Published: 17 May 2017
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Abstract
The construction of Pohang Accelerator Laboratory X-ray Free-Electron Laser (PAL-XFEL), a 0.1-nm hard X-ray free-electron laser (FEL) facility based on a 10-GeV S-band linear accelerator (LINAC), is achieved in Pohang, Korea by the end of 2016. The construction of the 1.11 km-long building
[...] Read more.
The construction of Pohang Accelerator Laboratory X-ray Free-Electron Laser (PAL-XFEL), a 0.1-nm hard X-ray free-electron laser (FEL) facility based on a 10-GeV S-band linear accelerator (LINAC), is achieved in Pohang, Korea by the end of 2016. The construction of the 1.11 km-long building was completed by the end of 2014, and the installation of the 10-GeV LINAC and undulators started in January 2015. The installation of the 10-GeV LINAC, together with the undulators and beamlines, was completed by the end of 2015. The commissioning began in April 2016, and the first lasing of the hard X-ray FEL line was achieved on 14 June 2016. The progress of the PAL-XFEL construction and its commission are reported here. Full article
(This article belongs to the Special Issue X-Ray Free-Electron Laser)
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Open AccessArticle Two- and Three-Photon Partial Photoionization Cross Sections of Li+, Ne8+ and Ar16+ under XUV Radiation
Appl. Sci. 2017, 7(3), 294; doi:10.3390/app7030294
Received: 14 February 2017 / Revised: 7 March 2017 / Accepted: 9 March 2017 / Published: 17 March 2017
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Abstract
In this work, we present the photon energy dependence of the two- and three-photon cross sections of the two-electron Li+, Ne8+ and Ar16+ ions, following photoionization from their ground state. The expressions for the cross sections are based on
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In this work, we present the photon energy dependence of the two- and three-photon cross sections of the two-electron Li+, Ne8+ and Ar16+ ions, following photoionization from their ground state. The expressions for the cross sections are based on the lowest-order (non-vanishing) perturbation theory for the electric field, while the calculations are made with the use of an ab initio configuration interaction method. The ionization cross section is dominated by pronounced single photon resonances in addition to peaks associated with doubly excited resonances. In the case of two-photon ionization, and in the non-resonant part of the cross section, we find that the 1D ionization channel overwhelms the 1S one. We also observe that, as one moves from the lowest atomic number ion, namely Li+, to the highest atomic number ion, namely Ar16+, the cross sections generally decrease. Full article
(This article belongs to the Special Issue X-Ray Free-Electron Laser)
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Review

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Open AccessFeature PaperReview Ultrashort Free-Electron Laser X-ray Pulses
Appl. Sci. 2017, 7(9), 915; doi:10.3390/app7090915
Received: 28 July 2017 / Revised: 29 August 2017 / Accepted: 30 August 2017 / Published: 6 September 2017
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Abstract
For the investigation of processes happening on the time scale of the motion of bound electrons, well-controlled X-ray pulses with durations in the few-femtosecond and even sub-femtosecond range are a necessary prerequisite. Novel free-electron lasers sources provide these ultrashort, high-brightness X-ray pulses, but
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For the investigation of processes happening on the time scale of the motion of bound electrons, well-controlled X-ray pulses with durations in the few-femtosecond and even sub-femtosecond range are a necessary prerequisite. Novel free-electron lasers sources provide these ultrashort, high-brightness X-ray pulses, but their unique aspects open up concomitant challenges for their characterization on a suitable time scale. In this review paper we describe progress and results of recent work on ultrafast pulse characterization at soft and hard X-ray free-electron lasers. We report on different approaches to laser-assisted time-domain measurements, with specific focus on single-shot characterization of ultrashort X-ray pulses from self-amplified spontaneous emission-based and seeded free-electron lasers. The method relying on the sideband measurement of X-ray electron ionization in the presence of a dressing optical laser field is described first. When the X-ray pulse duration is shorter than half the oscillation period of the streaking field, few-femtosecond characterization becomes feasible via linear streaking spectroscopy. Finally, using terahertz fields alleviates the issue of arrival time jitter between streaking laser and X-ray pulse, but compromises the achievable temporal resolution. Possible solutions to these remaining challenges for single-shot, full time–energy characterization of X-ray free-electron laser pulses are proposed in the outlook at the end of the review. Full article
(This article belongs to the Special Issue X-Ray Free-Electron Laser)
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Open AccessReview The Linac Coherent Light Source: Recent Developments and Future Plans
Appl. Sci. 2017, 7(8), 850; doi:10.3390/app7080850
Received: 31 July 2017 / Accepted: 10 August 2017 / Published: 18 August 2017
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Abstract
The development of X-ray free-electron lasers (XFELs) has launched a new era in X-ray science by providing ultrafast coherent X-ray pulses with a peak brightness that is approximately one billion times higher than previous X-ray sources. The Linac Coherent Light Source (LCLS) facility
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The development of X-ray free-electron lasers (XFELs) has launched a new era in X-ray science by providing ultrafast coherent X-ray pulses with a peak brightness that is approximately one billion times higher than previous X-ray sources. The Linac Coherent Light Source (LCLS) facility at the SLAC National Accelerator Laboratory, the world’s first hard X-ray FEL, has already demonstrated a tremendous scientific impact across broad areas of science. Here, a few of the more recent representative highlights from LCLS are presented in the areas of atomic, molecular, and optical science; chemistry; condensed matter physics; matter in extreme conditions; and biology. This paper also outlines the near term upgrade (LCLS-II) and motivating science opportunities for ultrafast X-rays in the 0.25–5 keV range at repetition rates up to 1 MHz. Future plans to extend the X-ray energy reach to beyond 13 keV (<1 Å) at high repetition rate (LCLS-II-HE) are envisioned, motivated by compelling new science of structural dynamics at the atomic scale. Full article
(This article belongs to the Special Issue X-Ray Free-Electron Laser)
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Open AccessReview Probing Physics in Vacuum Using an X-ray Free-Electron Laser, a High-Power Laser, and a High-Field Magnet
Appl. Sci. 2017, 7(7), 671; doi:10.3390/app7070671
Received: 31 March 2017 / Revised: 27 June 2017 / Accepted: 28 June 2017 / Published: 29 June 2017
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Abstract
A nonlinear interaction between photons is observed in a process that involves charge sources. To observe this process in a vacuum, there are a growing number of theoretical and experimental studies. This process may contain exotic contribution from new physics beyond the Standard
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A nonlinear interaction between photons is observed in a process that involves charge sources. To observe this process in a vacuum, there are a growing number of theoretical and experimental studies. This process may contain exotic contribution from new physics beyond the Standard Model of particle physics, and is probed by experiments using a high-power laser or a high-field magnet, and more recently using an X-ray free-electron laser (XFEL). Here, we review the present status of our experiments testing various vacuum processes. We describe four experiments with a focus on those using an XFEL: (i) photon–photon scattering in the X-ray region, (ii) laser-induced birefringence and diffraction of X rays, (iii) vacuum birefringence induced by a high-field magnet, and (iv) a dedicated search for axion-like particles using the magnet and X rays. Full article
(This article belongs to the Special Issue X-Ray Free-Electron Laser)
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Open AccessReview Measurement of the Resonant Magneto-Optical Kerr Effect Using a Free Electron Laser
Appl. Sci. 2017, 7(7), 662; doi:10.3390/app7070662
Received: 1 June 2017 / Revised: 20 June 2017 / Accepted: 21 June 2017 / Published: 27 June 2017
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Abstract
We present a new experimental magneto-optical system that uses soft X-rays and describe its extension to time-resolved measurements using a free electron laser (FEL). In measurements of the magneto-optical Kerr effect (MOKE), we tune the photon energy to the material absorption edge and
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We present a new experimental magneto-optical system that uses soft X-rays and describe its extension to time-resolved measurements using a free electron laser (FEL). In measurements of the magneto-optical Kerr effect (MOKE), we tune the photon energy to the material absorption edge and thus induce the resonance effect required for the resonant MOKE (RMOKE). The method has the characteristics of element specificity, large Kerr rotation angle values when compared with the conventional MOKE using visible light, feasibility for M-edge, as well as L-edge measurements for 3d transition metals, the use of the linearly-polarized light and the capability for tracing magnetization dynamics in the subpicosecond timescale by the use of the FEL. The time-resolved (TR)-RMOKE with polarization analysis using FEL is compared with various experimental techniques for tracing magnetization dynamics. The method described here is promising for use in femtomagnetism research and for the development of ultrafast spintronics. Full article
(This article belongs to the Special Issue X-Ray Free-Electron Laser)
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Open AccessFeature PaperReview Status of the SACLA Facility
Appl. Sci. 2017, 7(6), 604; doi:10.3390/app7060604
Received: 12 May 2017 / Revised: 7 June 2017 / Accepted: 8 June 2017 / Published: 10 June 2017
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Abstract
This article reports the current status of SACLA, SPring-8 Angstrom Compact free electron LAser, which has been producing stable X-ray Free Electron Laser (XFEL) light since 2012. A unique injector system and a short-period in-vacuum undulator enable the generation of ultra-short coherent X-ray
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This article reports the current status of SACLA, SPring-8 Angstrom Compact free electron LAser, which has been producing stable X-ray Free Electron Laser (XFEL) light since 2012. A unique injector system and a short-period in-vacuum undulator enable the generation of ultra-short coherent X-ray pulses with a wavelength shorter than 0.1 nm. Continuous development of accelerator technologies has steadily improved XFEL performance, not only for normal operations but also for fast switching operation of the two beamlines. After upgrading the broadband spontaneous-radiation beamline to produce soft X-ray FEL with a dedicated electron beam driver, it is now possible to operate three FEL beamlines simultaneously. Beamline/end-station instruments and data acquisition/analyzation systems have also been upgraded to allow advanced experiments. These efforts have led to the production of novel results and will offer exciting new opportunities for users from many fields of science. Full article
(This article belongs to the Special Issue X-Ray Free-Electron Laser)
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Open AccessFeature PaperReview Molecular Dynamics of XFEL-Induced Photo-Dissociation, Revealed by Ion-Ion Coincidence Measurements
Appl. Sci. 2017, 7(5), 531; doi:10.3390/app7050531
Received: 24 March 2017 / Revised: 25 April 2017 / Accepted: 12 May 2017 / Published: 19 May 2017
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Abstract
X-ray free electron lasers (XFELs) providing ultrashort intense pulses of X-rays have proven to be excellent tools to investigate the dynamics of radiation-induced dissociation and charge redistribution in molecules and nanoparticles. Coincidence techniques, in particular multi-ion time-of-flight (TOF) coincident experiments, can provide detailed
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X-ray free electron lasers (XFELs) providing ultrashort intense pulses of X-rays have proven to be excellent tools to investigate the dynamics of radiation-induced dissociation and charge redistribution in molecules and nanoparticles. Coincidence techniques, in particular multi-ion time-of-flight (TOF) coincident experiments, can provide detailed information on the photoabsorption, charge generation, and Coulomb explosion events. Here we review several such recent experiments performed at the SPring-8 Angstrom Compact free electron LAser (SACLA) facility in Japan, with iodomethane, diiodomethane, and 5-iodouracil as targets. We demonstrate how to utilize the momentum-resolving capabilities of the ion TOF spectrometers to resolve and filter the coincidence data and extract various information essential in understanding the time evolution of the processes induced by the XFEL pulses. Full article
(This article belongs to the Special Issue X-Ray Free-Electron Laser)
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Other

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Open AccessFeature PaperProject Report Status of the SXFEL Facility
Appl. Sci. 2017, 7(6), 607; doi:10.3390/app7060607
Received: 24 April 2017 / Revised: 5 June 2017 / Accepted: 6 June 2017 / Published: 12 June 2017
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Abstract
The Shanghai soft X-ray Free-Electron Laser facility (SXFEL) is being developed in two steps; the SXFEL test facility (SXFEL-TF), and the SXFEL user facility (SXFEL-UF). The SXFEL-TF is a critical development step towards the construction a soft X-ray FEL user facility in China,
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The Shanghai soft X-ray Free-Electron Laser facility (SXFEL) is being developed in two steps; the SXFEL test facility (SXFEL-TF), and the SXFEL user facility (SXFEL-UF). The SXFEL-TF is a critical development step towards the construction a soft X-ray FEL user facility in China, and is under commissioning at the Shanghai Synchrotron Radiation Facility (SSRF) campus. The test facility is going to generate 8.8 nm FEL radiation using an 840 MeV electron linac passing through the two-stage cascaded HGHG-HGHG or EEHG-HGHG (high-gain harmonic generation, echo-enabled harmonic generation) scheme. The construction of the SXFEL-TF started at the end of 2014. Its accelerator tunnel and klystron gallery were ready for equipment installation in April 2016, and the installation of the SXFEL-TF linac and radiator undulators were completed by the end of 2016. In the meantime, the SXFEL-UF, with a designated wavelength in the water window region, began construction in November 2016. This was based on upgrading the linac energy to 1.5 GeV, and the building of a second undulator line and five experimental end-stations. Construction status and the future plans of the SXFEL are reported in this paper. Full article
(This article belongs to the Special Issue X-Ray Free-Electron Laser)
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Open AccessMeeting Report Nobel Symposium on Free Electron Laser Research
Appl. Sci. 2017, 7(4), 408; doi:10.3390/app7040408
Received: 5 April 2017 / Revised: 17 April 2017 / Accepted: 17 April 2017 / Published: 18 April 2017
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Abstract
This meeting report describes the Nobel Symposium on Free Electron Laser Research, which was organized in Sigtuna, Sweden, 14–18 June 2015. Full article
(This article belongs to the Special Issue X-Ray Free-Electron Laser)

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